"[Paddy] has a history with Cavanaugh, it turns out, and that is a major reason Maura has to take a step back and choose a side: her biological family or her professional family," Alexander tells TVGuide.com. "Whether what happened [between Paddy and Cavanaugh] was done consciously, it's just more proof that Paddy's done enormously shady things in his life and he's not a man that you can trust."What do you think their past is? Might it have something to do with how Cavanaugh's wife and son died in a house fire back in the day?Rizzoli & Isles